Currently there's an issue with this achievement meaning that if you do the Bloodsail Buccaneers first, and then farm up Steamwheedle, it unflags Bloodsail from the criteria, which makes the achievement harder than it should be. We have received a few reports about this, and it's something we are investigating, and shall fix as soon as possible.

TLDR: If you want to make sure you will get the achievement, leave Bloodsail to last. This is probably not the answer you wanted, but at least you know what's going on.

I investigated this further for you. At the moment, you'll either need to wait for this to be fixed (it's being looked into as I said), or, do Bloodsail last. I'm afraid there's nothing we can do at this moment and sadly there's no ETA for a fix.